Stabilization of lubricants



Delaware No Drawing. Filed Nov. 19, 1962, Ser. No. 238,772

9 Claims. (Cl. 252-515) This is a continuation-in-part of my co'pending application Serial No. 48,814, filed August 11, 1960, now Patent 3,093,586, issued June 11, 1963, which, in turn, is a continuation-in-part of application Serial No. 826,403, filed July 13, 1959, now Patent 3,078,230, issued February 19, 1963, and relates to the stabilization of lubricants and, more particularly, to a synergistic inhibitor composition and to the use thereof as an additive in lubricants.

In recent years, stringent requirements for lubricants in Certain applications have resulted in the availability of a new class of lubricants referred to in the art as synthetic lubricants. T hose lubricants do not necessarily replace petroleum oils in conventional usage, but are designed for special applications where the petroleum oils do not function to a satisfactory degree. These synthetic lubricants have found particular use in winter-grade crankcase oils, turbo-engine oils, aviation instruments, automatic weapons, etc. For example, aircraft gas turbines require oils capableof providing satisfactory lubrication at temperatures ranging as low as -65 F. and as high as 425 F. during use. Temperatures up to 600 F. are encountered for intervals of from one to two hours during shut-down. Petroleum lubricants are unsatisfactory at high altitudes or in the winter season for use in machine guns and automatic cannons which frequently could not be made to fire because of congealed lubricants. Because they are used under such stringent conditions, the synthetic lubricants may undergo undesirable deterioriation including, for example, formation of deposits, discoloration, change of viscosity, etc. While the features of the present invention are particularly applicable to the stabilization of synthetic lubricants, it is understood that they also may be used for the stabilization of petroleum lubricants.

The synthetic lubricants are of varied types including aliphatic esters, polyalkylene oxides, silicones, esters of phosphoric and silicic acids, highly fluorine-substituted hydrocarbons, etc. Of the aliphatic esters, di-(2-ethylhexyl)sebacate is being used on a comparatively large commercial scale. Other aliphatic esters include dialkyl azelates, dialkyl suberates, dialkyl pimelates, dialkyl adi-,

pates, dialkyl glutarates, etc. Specific examples of these esters include dihexyl azelate, di-(2-ethylhexyl)azelate, di- 3,5,5-trimethylhexyl glutarate, di-3,5,5-trimethylpentyl glutarate, di-(Z-ethylhexyl)pimelate, di-(2-ethylhexyl)adipate, triamyl tricarballylate, pentaerythritol tetracaproate, dipropylene glycol dipelargonate, 1.5-pentanediol-di-(2- ethylhexanonate), etc. The polyalkylene oxides include polyisopropylene oxide, polyisopropylene oxide diether, polyisopropylene oxide dicstcr, etc. The silicones include methyl silicone, methylphenylsilicone, etc., and the silicates include, for example, tetraisooctyl silicate, diphenyl di-n-dodecyl silane, octadecyl tri-n-dccyl silane, polysilylmethylenes, silophenylene, various silane mixtures, silicone-ester blends, etc. The highly fiuorinated hydrocarbons include fiuorinated oil, perfiuorohydrocarbons, etc.

Additional synthetic lubricating oils include (1) neopentyl glycol esters in which the ester group contains from 3 to 12 carbon atoms or more, and particularly neopentyl glycol propionates, neopentyl glycol butyrates, neo

United States Patent pcntyl glycol caproatcs, neopentyl glycol caprylates, neo pentyl glycol pelargonates, etc., (2) trimethylol alkanes such as trimethylol ethane, tl'imethylol propane, trimethylol butane, trimethylol pentan'e, trimethylol hexane, trimethylol heptane, trimethylol octane, trimethylol decane, trimethylol undecane, trimethylol dodecane, etc., as well as the esters thereof and particularly triesters in which the ester portions each contain from 3 to 12 carbon atoms and may be selected from those hereinbefore specifically set forth in connection with the discussion of the neopentyl glycol esters, and (3) tricresylphosphate, trioctylphosphate, trinonylphosphate, tridecylphosphate, as well as mixed aryl and alkyl phosphates, etc.

The lubricating oils of petroleum origin include those referred to as motor lubricating oil, railroad type lubricating oil, marine oil, transformer oil, turbine oil, transmission oil, differential oil, diesel lubricating oil, gear oil, cutting oil, rolling oil, cylinder oil, hydraulic oil, sloshing oil, specialty products oil, etc.

The present invention also is applicable to the stabilization of greases made by compositing metallic soaps with the synthetic lubricating oils described above and are referred to herein as synthetic greases. These metal base synthetic greases may be further classified as lithium base synthetic grease, sodium base synthetic grease, calcium base synthetic grease, barium base synthetic grease, strontium base synthetic grease, aluminum base synthetic grease, barium complex greases, calcium complex greases, sodium-calcium greases, lithium-l2-hydroxy stcarate greases, lithium-calcium greases, calcium-lead greases, etc. These greases are solid or semi-solid gels are prepared by the addition to the synthetic lubricating oil of hydrocarbon-soluble metal soap or salts of higher fatty acids as, for example, lithium stearate, calcium stearate, aluminum naphthenate, etc. The grease may contain thickening agents such as silica, carbon black, talc,

organic modified Bentonite, etc., polyacrylates, amides, polyamides, aluminum imides, phthalocyanines, oxanilides, complex aromatic imides and amides, hydantoin derivatives, benzidine dyes, aryl ureas, methyl N-n-octadecyl terephthalomate, etc. Another type of grease is prepared from oxidized petroleum wax, to which the saponifiable base is combined with the proper amount of the desired saponifying agent, and the resultant mixture processed to produce a grease. Other types of greases in which the features of the present invention are usable in clude petroleum grease, whale grease, wool grease, etc., and those made from inedible fats, tallow, butchers waste, etc.

It is general practice to incorporate an anti-oxidant in synthetic lubricants in order to improve the stability thereof. Research continues to search for even better inhibitors in order to further improve the synthetic lubricants and permit their use for longer periods of time in present applications, as well as to permit their use under even more severe conditions as, for example, in the engines of the future which are being developed to operate at peak efficiency at high altitudes. It is important that the synthetic lubricant under these conditions is stable, retains its lubricity properties, does not develop deposit formation, retains its desirable viscosity, etc.

It now has been found that a synergistic composition of both an antioxidant and certain nitrogen-containing polymers impart to the synthetic lubricant a considerably improved stability, much greater than obtained through the use of the antioxidants alone. In fact, this synergistic effect is surprising because the polymers themselves do not improve the stability of the synthetic lubricant to and, in general,

any substantial extent. Normally it would be predicted that this mixture would not be any better than the antioxidant alone. Accordingly, it is surprising that these great improvements in the stability of the lubricant are obtained through the use of the novel inhibitor mixture of the present invention.

In one embodiment the present invention relates to a method of stabilizing a lubricant which comprises incorporating therein a stabilizing concentration, in a synergistic proportion, of: a diaminodiphenyl ether antioxidant and a synergist comprising a polymeric condensation product of an acrylzitc and an alkylaminoalkyl acrylate.

la a specific embodiment the present invention relates to a method of stabilizing di-(Z-ethylhexyl)sebacate which comprises incorporating therein a stabilizing concentra tion, in a synergistic proportion, of 2,4-di-sec-butyl-diaminodiphcnyl ether and a polymeric condensation product of lauryl methacrylate and beta-diethylaminoethyl methacrylate.

In another specific embodiment the present invention relates to a method of stabilizing lithium base grease which comprises incorporating therein a stabilizing concentration, in a synergistic proportion, of 4,4'-di-sec-butyl-diaminodiphenyl ether and a polymeric condensation product of n-octyl methacrylate and beta-diethylaminoethyl methacrylate.

Any suitable diaminodiphenyl ether is used as the antioxidant component of the inhibitor composition. 'Preferred diaminodiphcnyl ethers include N,N'-diisopropyldiaminodiphenyl ether, N,N-di-secbutyl-diaminodiphenyl ether, N,N-di-sec'amyl-diaminodiphenyl ether, N,N- di-sec-hexyl-diaminodiphenyl ether, N,N'-di-sec-heptyldiaminodiphenyl ether, N,N'-di-sec-octyl-diaminodiphenyl ether, N,N-di-sec-nonyldiaminodiphenyl ether, N,N-disec-decyl-diaminodiphenyl ether, N .N'-di-sec-undecyl-diaminodiphenyl ether, 'N,N'-di-sec-dodeeyl-diaminodiphenyl ether, N,N'-di-sec-tridecyl-diaminodiphenyl ether, N, N'-di-sec-tetradecyl-diaminodiphenyl ether, etc. Other antioxidants include N,N-di-cyclohexyl diaminodiphenyl ether and alkylated derivatives thereof. The amino groups are preferably in the 4,4'- and/or 2,4'-positions.

In another embodiment the diaminodiphenyl ether antioxidant is an aminophenyl alkox-yphenyl ether. Illustrative preferred antioxidants in this embodiment include 4- methoxyphenyll-amiuophenyl ether, 4-methoxyphenyl- 4-N-methyl-aminophenyl ether, 4-methoxyphenyl-4-N- ethyl-aminophenyl ether, 4-rnethoxyphenyl-4'-N-isopr0- pyl-arninophenyl ether, 4-methoxyphenyl-4'-N-sec-butylaminophenyl ether, 4-methoxyphenyl-4'-N-sec-arnyl-aminophenyl ether, 4-rnethoxyphcnyl 4 cyclohexyl-aminophenyl ether, etc., 4-methoxyphenyl2'-'1rninophenyl ether, 4-mcthoxyphenyl-2'-N-rnethylaminophenyl ether, 4-methoxyphenyl-Z'-N-ethyl aminophenyl ether, 4 methoxyphcnyl-2-N-isopropyl-aminophenyl ether, 4-methoxypheny]-2-N-sec-butyl-aminophenyl ether, 4-methoxyphenyl-2- N-sec-amyl-aminophenyl ether, 4-methoxyphenyl-2'-N-cyclohexyl-aminophenyl ether, etc., 2-methoxyphenyl-4'- aminophenyl ether, 2-niethoxyphenyl-4-N-methyl-aminophenyl ether, 2 methoxyphenyl 4 ethyl-aminophenyl ether, 2 methoxyphenyl 4 N-isopropyl-arninophenyl ether, Z-methoxyphenyl-4'-N-sec-butyl-aminophenyl ether, 2-methoxyphenyl- 4' -N-sec-amyl-aminophenyl ether, 2- methoxyphenyl-4-N-cyclohexyl-aminophenyl ether, etc.

Illustrative compounds containing two alkoxy groups include 2,6-dimethoxyphenyl-4'-aminophcnyl ether, 2,4- dimethoxyphenyl-4'-aminophenyl ether, 3,4-dirnethoxyphenyl-4'-aminophenyl ether, 2,4 dimethoxyphenyl 2'- aminophenyl ether, 3,4-dimethoxyphenyl-2'-aminophenyl ether, etc., and similar compounds in which a hydrocarbon substituent is attached to the nitrogen atom, the hydrocarbon substituent preferably being selected from those hereinbefore set forth. Illustrative examples containing hydrocarbon substitueats attached directly to the nucleus of one or both of the phenyl rings include 2- methoxy-4 methylphenyl-4-aminophcnyl ether, 4-inethox- 4 y-2-methylphenyl-4'-aminophcnyl ether, 2,6 dimcthoxy- 4-methylplicnyl-4' aminophenyl e-thcr, 2-mcthyl-4-mcthoxyphcnyl '2 aminophenyl ether, 2 methyl 4,6-dimcthoxyphenyl-2'aminophenyl ether, etc. lt is understood that other hydrocarbon groups and particularly those hcreinbetorc set forth may be substituted for the methyl group and also that the nitrogen atom may contain a hydrocarbon constituent attached thereto, the latter substituent preferably being selected from those hereinbefore set forth.

It is understood that different antioxidants are not necessarily equivalent, but all of them will form a synergistic mixture with the acrylate-alkylaminoalkyl acrylate condensation product and will produce improved benefits over and above those expected from the use of either componcnt separately.

The polymeric condensation product for use in the synergistic mixture is produced by the polymeric condensation of an unsaturated compound having a polymerizable ethylenic linkage and an unsaturated compound having a polymerizable ethylenic linkage and a basic nitrogen. In a preferred embodiment the first-mentioned unsaturated compound is amine free and contains from 8 to 18 carbon atoms in an acyclic chain. Examples of such compounds include saturated and unsaturated long chain esters of unsaturated carboxylic acids such as 2- ethylhexyl acrylate, nonyl acrylate, decyl acrylate, undecyl acrylate, dodecyl acrylate, tridecyl acrylate, tetradecyl acrylate, pentadecyl acrylate, hexadecyl acrylate, heptadecyl acrylate, octadecyl acrylate, etc., and particularly methacrylates including n-octyl methacrylate, n-nonyl methacrylate, 3,5,5-trimethylhexyl methacrylate, n-decyl methacrylate, sec-capryl 'methacrylate, lauryl methacrylate, dodecyl methacrylate, tridecyl methaerylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, cetyl methacrylate, heptadecyl methacrylate, octadccyl methacrylate, 9-octadecenyl methacrylate, etc.; unsaturated esters of long-chain carboxylic acids such as vinyl laurate, vinyl stearate; long-chain esters of vinylcne dicarboxylic acids such as methyl lauryl fumarate; long-chain monoolefins such as the alkyl or acyl substituted styrenes as, for example, dodecyl styrene, and the like. A particularly preferred compound is lauryl methacrylate and more particularly technical lauryl methacrylate which is obtained by esterification of a commercial mixture of long-chain alcohols in the C to C range derived from coconut oil. The technical lauryl methacrylate is available commercially at a lower price and, accordingly, is preferred. A typical technical lauryl methaerylate will contain in the ester portion carbon chain lengths of approximately 3% C 61% C 23% C14, 11% C15, and 2% C13.

Examples of the second-mentioned unsaturated compounds (those containing a basic nitrogen) include p- (beta-diethylaminoethyl)-styrene; basic nitrogen-containing heterocycles carrying a polymerizable ethylenically unsaturated substituent such as the vinyl pyridines and the vinyl alkyl pyridines as, for example, Z-VinyIS-ethyl pyridine; esters of basic amino alcohols with unsaturated carboxylic acids such as the alkyl and cycloalkyl substituted aminoalkyl and aminocycloalkyl esters of the acrylic and alkacrylic acids as, for example, beta-methaminoethyl acrylate, beta-diethylaminoethyl methacrylate, 4-diethylaminocyclohexyl methacrylate, bta-betadidodecylami noethyl acrylate, ete.; unsaturated ethers of basic amino alcohols such as the vinyl ethers of such alcohols as, for example, beta-aminoethyl vinyl ether, beta-diethylaminoethyl vinyl ether, etc.; amides of unsaturated carboxylic acids wherein a basic amino substituent is carried on the amide nitrogen such as N-(bcta-dimethylaminoethyl)- acrylamide; polymerizable unsaturated basic amines such as diallylamine, and the like.

The above polymeric condensation product is prepared in any suitable manner and generally by heating the reactants at a temperature of from about to about about 10% having 80% 175 F. for a period of time ranging from two to fortyeight hours or more, preferably in the presence of a catalyst or initiator such as benzoyl-peroxide, tertiary butyl peroxide, azo compounds as alpha,alpha'-azo-diisobutyronitrile, etc. When desired, the polymerization may be effected in the presence of a solvent and particularly aromatic hydrocarbons, including, for example, benzene, toluene, xylene, cumene, decalin, naphtha, etc. In general the condensation is elfected using the first-mentioned and the second-mentioned unsaturated compounds in proportions to produce a copolymer containing from about 50% to about 95% and preferably from about 70% to about 90% by weight of the first-mentioned compound and from about 5% to about 50% and preferably from to about 30% by weight of the second-mentioned compound.

The proportions of antioxidant and synergist may vary over a wide range and thus may range from 0.1 to 4 and preferably from 0.5ito 2 parts by weight of synergist per one part by weight of antioxidant, although in some cases lower or higher proportions may be used. These pro portions are based upon the active ingredient exclusive of solvent. While the antioxidant and synergist may be added separately to the lubricant .-it generally is preferred to form a suitable mixture of the antioxidant and synergist and add the mixtureto the lubricant. When desired, the antioxidant and synergist may be prepared as a solution in asuitable solvent, particularly aromatic hydrocarbons and more particularly an aromatic hydrocarbon as hereinbefore set forth, and marketed or used as a single product. Conveniently, the same solvent is used in the final solution as used in the preparation of one or both of the antioxidant and synergist. The solution may comprise from about to about 90% and preferably from about 25% to about 75% by weight of active ingredient.

The inhibitor composition will be used in the substrate in an amount sufiicient to obtain the desired stabilization. This stabilizing concentration will be within the range of from about 0.01% to about and preferably from about 0.1% to about 5% by weight of the lubricant. The inhibitor composition is added to the lubricant in any suitable manner and preferably with intimate mixing in order. to obtain distribution of the inhibitor composition in the lubricant. In some cases the inhibitor composition may be added to the lubricant during the manufacture thereof. For example, when used in grease, the inhibitor composition may be added to one or more of the components before final compositing thereof.

It is understood that the inhibitor composition of the present invention may be used along with other additives incorporated in the lubricant. For example, a metal deactivator, dye, viscosity index improver, pourpoint depressant, antifoaming additive, lubricity and extreme pressure additive, antiscutfing additive, antifriction additive, antiwear additive, detergent-dispersant, etc., may be incorporated in the synthetic lubricant. When desired, the inhibitor composition of the present invention may be prepared as a mixture with one or more of these other additives and incorporated in this manner in the lubricant.

The following examples are introduced to illustrate further the novelty and utility of the present invention but not with the intention of unduly limiting the same.

EXAMPLE I The polymeric condensation product is prepared by copolymerizing lauryl methacrylate and diethylaminoethyl methacrylate in concentrations to yield a product by weight of lauryl methacrylate and by weight of diethylaminoethyl methacrylate. The polymerization is effected by heating the reactants at about 140 -F. for about eighteen hours, with vigorous stirring in the presence of benzyl peroxide catalyst. The product is recovered as a straw colored, heavy viscous oil of the general properties set forth in Table I.

- sludge and varnish formation maintained at 400 F. and air is blown I Table I Viscosity at 210 F., SSU 2200 .v Density, pounds/gallon 7.5. Color, N.P.A. 1. Pour point, F. -10 to +10. Flash point (COC), F 380. Fire point (COC), F. 420. Total acidity 0.0. I Total base No., mg. KOl-I/g 8.0 (0.14 meq./g.). Ash, weight ercent 0.00.

EXAMPLE II As hereinbefore set forth, the improved results obtained by using the mixture of the present invention are surprising because the polymeric condensation product itself is not an inhibitor. This is shown by the data in the following table, which were obtained in the following manner. The polymeric condensation product was evaluated in dioctyl sebacate, marketed under the trade name of Plexol 201. The evaluation was made in accordance with an Oxygen Stability Test in which a cc. sample of the synthetic lubricating oil is placed in a bath therethrough at a rate of 5 liters of air per hour. The sample of synthetic lubricating -oil is examined periodically and the time to reach an acid number of 5 is reported. It is apparent that the longer the time required to reach an acid number of 5 the more stable is the sample of synthetic lubrieating oil. In other words, it takes longer for the more stable oil to deteriorate.

Table II Hours to acid Additive: number of 5 None 9 1% by weight of the polymeric condensation product of Example I 10 From the above data it will be seen that the polymeric condensation product itself was not effective to extend the time required to reach an acid number of 5.

EXAMPLE III The synergistic mixture of this example is a mixture of 2,4-di-sec-butyl-diaminodiphenyl ether and the polymeric condensation product of Example I. When evaluated in another sample of the dioctyl sebacate described in Exampte I, the diaminodiphenyl ether, in a concentration of 1% by weight, increases the time to an acid number of 5 from 9 hours to 35 hours. However, the synergistic mixture of 1% by weight of the diaminodiphenyl ether and 1% by weight of the condensation product of Example I increases the time to reach an acid number of 5 to more than 50 hours.

EXAMPLE IV Another advantage of the synergistic mixture of the present invention is that it also considerably reduces as a result of inhibiting deterioration of the lubricating oil during use. The following data reports results in a Chevrolet L-4 test. This test is run using an engine speed of 3150 r.p.m., an engine load of 30 B.H.P., a jacket outlet temperature of 210 F., a jacket inlet temperature of R, an oil temperature of 280 F. and an air fuel ratio of 14.5:1. Regular grade gasoline and Mid-Continent solvent refined lubricating oil are used. Each run is continued for 36 hours.

The synergistic mixture of weight of a mixture of 70% by weight of 2,4-di-sec-butyldiaminodiphenyl ether and 30% by weight of 4,4'-di-secbutyl-diaminodiphenyl ether and 1% by weight of the polymeric condensation product of Example I.

The following table reports the results of three runs conducted in the manner described above. In the first run (Run A), no additive was incorporated in the lubrithis example is 0.5% by S.A.E. 20 type eating oil. In the second run (Run B). 0.5% by weight of the mixture ol 70% by weight of 2.4-di-scc-butyldi'aminodiphenyl ether and 30% by weight of 4.4'di-secbutyl-diaminodiphcnyl ether was incorporated in the abricating oil. In the third run Run C), a synergistic mixture of 0.5% by weight of. the mixture of 70% by weight of 2,4'-di-scc-butyl-diaminodiphenyl ether and 30% by weight of 4.4-di-sec-hutyl-diaminodiphenyl ether and 1% by weight of the polymeric condensation product of Example I was incorporated in the lubricating oil.

Pertinent data of these runs are reported in the following table:

Tub/1' Ill Ituu A iNoAd- Run lil nni Ili'n t a: rer' tiitiw) iinuli i' ixl gi iicniixiiir-al ctbri') 117W 1.7157 'lu ul \zlrhi l and sludge, gravi i'ic,

gran s ll ursilu to ext-issue .\t i hrs. ,lt Fihrs. .\t I lzr Lst-il all analyses:

lentane insolublis. wt. percent. (l, 4 til h. 786 3T0 Benzene insolnbles.

\i't. p rcent 0. .237 0.: ll 0. 243

Insoluble Ft \\'t.i elit'nt 0.212 0.1151 RS1 l" till: 33h 3.71

From the above table. it will be seen that the synergistic mixture served to improve the operation of the engine as compared to the run without inhibitor and to the run made with the diaminodiphenyl ether alone.

Of special importance is the considerably lower amount of total varnish and sludge. be discontinued after 12 hours.

It will be noted that Run A had to In Run B, the total varnish and sludge was greater than 7 grams, whereas it was less than 2 grams in mixture.

of Example I.

EXAMPLE V The synergistic mixture of this example comprised 0.5% by Weight of 2,4'-di-sec-butyl-diaminodiphenyl ether and 1% by weight of the polymeric condensation product Run C using the synergistic The results of runs made in the same manner as described in Example IV are reported in the following Here again, it is seen that the synergistic mixture of the present invention considerably improved the operation of the engine and inhibited deterioration of the lubricating oil during use.

8 11mm ll e V1 As hercinbcfore set forth, the cleanliness of the oil during use is very important and could mean the difference between an additive which would be acceptable and one which would not be acceptable. The cleanliness is evaluated by determining the percent isooetane insolublcs, the percent viscosity change and the appearance of the tube after use. The following table reports results made in dioctyl sebacate evaluated in the stability test described in Example II in which the determinations were made after 48 hours exposure and the viscosity change was determincd at 130 F. In these tests. 2% by weight of the additives were used. These data are reported in the following table:

Table V P rcent lsooctane ierc nt av Insolubles" Change Additive Tube Appearance Determined after 48 hours.

Here again, the synergistic effect is clearly demonstrated. It normally would be expected that the percent isooctane insolubles would be an average of the total of those obtained with each additive alone (l.53+9.23 =10.76 which, divided by 2, gives an average of 5.38 isooctane insolubles). It will be noted that the percent isooctane insolubles formed when using the mi ture amounts to only 1.7%. The same applies to the percent viscosity change which normally would be expected to be about 90% (16+165:18l divided by 2:90). instead, and surprisingly, the viscosity change is only 4.3% when using the mixture of additives. The same also applies to the appearance of the tube. Certainly, it one of the additives forms varnish and deposits when used alone, it would be expected that a mixture including such additive would likewise do so. However, as shown by the above data, the expected result did not occur but instead the tube was clean.

EXAMPLE VII As hereinbefore set forth, a synthetic lubricant being considered for use at high temperature is pentacrythritol ester. The pentaerythritol ester used in this example is available commercially from Hercules Powder Company as Hcrcollcx 600" and is stated to be monomeric pentacrythritol ester having an acid number of. 0.10 maximum, 11 saponification number of 410, a refractive index at 20 C. of 1.453 and a specific gravity at 25/25 C. of 0.997.

The evaluations in the pentaerythritol ester are made in substantially the same manner as described in Example II for dioctyl sebacate. The synergistic inhibitor mixture of this example is 1% by weight of 4-methoxyphenyl-4- N-isopropyl-aminophcnyl ether and 1% by weight of the polymeric condensation product of Example I.

When evaluated in the pcntaerythritol ester in the same manner as described for the dioctyl sebacate, except conducted at 500 F. instead of 400 F., the synergistic mixture had a longer time to acid number of 5 than obtained with either component alone. It was compared with a sample of the pentaerythritol ester containing 1% by Weight of the 4-methoxyphcnyl4'-l-isopropyl-aminophcnyl ether and with a separate sample containing 2% by weight of the polymeric condensation product of Example I. The percent isooctanc insolublcs was lower for the synergistic mixture than when using either component alone and, of particular importance, is the fact that the 9 percent viscosity change was 62% as compared to the viscosity change of 134% for the sample of lubricating oil containing the polymeric condensation product.

EXAMPLE VIII Specific gravity, 60/60 F. 0.965 Acidity, mg./KOI-I/ g. 0.03 Color, ASTM 2 Fire point, COC, F. 520 Flash point, COC, F. 460 Hydrolysis number 0.27 Viscosity:

At -65 F., cs. 14,900 At 100 F., SSU 76.93 At 210 F., SSU 37.77

The antioxidant, polymeric condensation product and synergistic mixture described in Example VII also were evaluated in the above synthetic lubricating oil. Here again, it is noted that the hours to acid number of 5 were greater for the synergistic mixture than were obtained with either of the components alone and also that the viscosity change was 34% as compared to 47% for the sample of lubricating oil. containing the antioxidant alone and 66% for the sample containing the polymeric condensation product alone.

EXAMPLE IX EXAMPLE X The synergistic inhibitor mixture of this example is 1.5% by weight of 4,4'-dicyclohexyl-diaminodiphenyl ether and 0.75% by weight of the polymeric condensation product formed by n-octyl-methacrylate and diethyl aminoethyl methacrylate.

When evaluated in the pentaerythritol esterhereinbefore described, the synergistic mixture serves to extend the induction period of the lubricating oil from 16 hours to more than 65 hours.

EXAMPLE XI The synergistic mixture of this example is 1% by Weight of 2,4'-di-sec-butyl-diaminodiphenyl ether and 0.5% by weight of the condensation product of Example I. It is utilized as an additive in lithium base grease.

The synergistic inhibitor mixture is incorporated in lubricating oil in the concentrations described above and the lubricating oil then is mixed with approximately 8% by weight of lithium stearate. The mixture is heated to about 450 F. with constant agitation. Subsequently the grease is cooled, while agitating, F. and then is further cooled slowly to room temperature.

to approximately 250v When evaluated in a bomb charged with oxygen at a temperature of 50 F., the induction period is determined as the time required for a drop of 5 pounds pressure to occur. The synergistic mixture serves to increase the induction period of the grease from 7 hours to over 200 hours.

I claim as my invention:

. 1. A synergistic inhibitor composition of 1 part by weight of N,N'-di-sec-butyl-diaminodiphenyl ether and from about 0.1 to about 4 parts by weight of the polymeric condensation product, formed at a temperature of from about 100 to about 175 F., of from about 50% to about by weight of lauryl methacrylate and from about 5% to about 50% by weight of beta-diethylaminoethyl methacrylate.

2. A synergistic inhibitor composition of 1 part by weight of N,N-dicyclohexyl-diaminodiphenyl ether and from about 0.1 to about 4 parts by weight of the polymeric condensation product, formed at a temperature of from about to about F., of from about 50% to about 95% by weight of lauryl methacrylate and from about 5% to about 50% by weight of beta-diethylaminoethyl methacrylate.

3. A synergistic inhibitor'composition of 1 part by I weight of 4-methoxyphenyl N-isopropylaminophenyl ether and from about 0.1 to about 4 parts by weight of the polymeric condensation product, formed at a temperature of from about 100 to about 175 F., of from about 50% to about 95% by weight of lauryl methacrylate and from about 5% to about 50% by weight of beta-diethylaminoethyl methacrylate.

4. A synergistic inhibitor composition of 1 part by weight of 4-methoxyphenyl N-sec-butylaminophenyl ether and from about 0.1 to about 4 .parts by weight of the polymeric condensation product, formed at a temperature of from about 100 to about 175 F., of from about 50% to about 95 by weight of lauryl methacrylate and from about 5% to about 50% by weight of beta-dicthylaminoethyl methacrylate.

5. A lubricating composition comprising a major proportion of a lubricant and from about 0.001% to about 5% by weight of the synergistic inhibitor composition of claim 1.

6. A lubricating composition comprising a major proportion of a lubricant and from about 0.001% to about 5% by weight of the synergistic inhibitor composition of claim 2.

7. A lubricating composition comprising a major proportion of a lubricant and from about 0.001% to about 5% by weight of the synergistic inhibitor composition of claim 3.

8. A lubricating composition comprising a major proportion of a lubricant and from about 0.001% to about 5% by weight of the synergistic inhibitor composition of claim 4.

9. A lubricating composition comprising a major pro-,

portion of dioctyl sebacate and from about 0.001% to about 5% by weight of the synergistic inhibitor composi-.

tion of claim 1.

DANIEL E. WYMAN, Primary Examiner. 

1. A SYNERGISTIC INHIBITOR COMPOSITION OF 1 PART BY WEIGHT OF N,N''-DIS-SEC-BUTYL-DIAMINODIPHENYL ETHER AND FROM ABOUT 0.1 TO ABOUT 4 PARTS BY WEIGHT OF THE POLYMERIC CONDENSATION PRODUCT, FORMED AT A TEMPERATURE OF FROM ABOUT 100* TO ABOUT 175*F., OF FROM ABOUT 50% TO ABOUT 95% BY WEIGHT OF LURYL METHACRYLATE AND FROM ABOUT 5% TO ABOUT 50% BY WEIGHT OF BETA-DIETHYLAMINOETHYL METHACRYLATE.
 5. A LUBRICATING COMPOSITION COMPRISING A MAJOR PROPORTION OF A LUBRICANT AND FROM ABOUT 0.001% TO ABOUT 5% BY WEIGHT OF THE SYNERGISTIC INHIBITOR COMPOSITION OF CLAIM
 1. 